Radio Frequency Identification (RFID) technology is fast becoming a part of our daily lives. These diverse devices and systems such as car immobilizers, access control systems, toll collection systems, global item tracking systems, and supply chain management rely more and more on RFID technology. RFID technology has been widely lauded for its potential to provide an unprecedented level of product traceability across the supply chain. RFID-enabled systems have the capability to greatly reduce human error from the data collection process. This error reduction, in turn, helps reduce inventories, improve product availability, identify and reduce loss and waste, and help ensure safety and security. All of these factors contribute to lower product cost and greater availability to consumers.
RFID transponders are typically manufactured and supplied in large quantities, often packaged in rolls ranging from 3 to 9 inches in diameter. Regardless of an RFID transponder's ultimate use or application, each must be converted from a blank transponder to one that carries an electronic ID code (i.e., is programmed). In the case of read-only transponders, a link between the transponder's internal ID code and the identity of the item that it is attached must recorded. Typically, this information is entered at the moment the transponder is peeled from the roll and attached to an item. This process is called data linking. Programming or data linking is typically performed before applying the transponders to items or shipping containers, etc. In the case of shipping labels, a shipper's address, the destination, and a routing number are often printed on a 4×6 inch label attached to an item (e.g., a package) over the transponders.
To work with the existing infrastructure of bar code scanners, the top side of each RFID-enabled shipping label must also be printed with both a bar code and human readable text to ensure compatibility with non-RFID enabled environments. Therefore, each of the many read-write or read-only transponders must be individually printed with a bar code representing a description of content, a shipping destination, etc. and then dispensed for attachment.
Typically, the blank transponders are supplied in either rolls or fan-fold stacks ready for printing. Since many blank transponders are packed in a limited space, an RFID reader/programmer must use a programming device that creates and projects a well-defined RF field. A well-defined field ensures that only a designated transponder is read and/or programmed while adjacent blank transponders are ignored. It is of particular importance that a neighboring transponder, which has already been programmed, not be erased or otherwise altered.
RFID transponders, especially those used at UHF frequencies, are specifically designed for a particular mounting surface. A transponder antenna designed for such UHF transponders must therefore be adjusted or tuned to ensure optimum performance when the transponder is mounted on its intended surface. A transponder that is designed or tuned for mounting on paper, for example, will have drastically reduced performance in free space conditions.
Depending on the specific design, when a transponder designed for paper mounting is unrolled and placed in free space and in preparation for reading/programming/printing, it can lose as much as 70% of its designed read range. The adjacent transponder(s) still on the paper roll, however, may retain full sensitivity. This degradation in read range between free space and paper, along with difficulty in controlling a programmer's antenna's read zone, accounts for some of the known reading/programming problems that must be reliably resolved.
When programming a transponder designed for paper mounting in free space, as is the case with most label printers, the programmer's field strength must be strong enough to compensate for the 70% degradation from paper to free space. Potential problems exist because other transponders still on the roll will typically have full sensitivity and may be within inches of the programming device. If the field strength outside the programming device is not controlled properly, the transponders still on the roll may receive sufficient signal strength to respond to a programming command that is intended for a free space transponder.
All programming commands are typically followed by a lock command. There is a need, therefore, for a transponder reading/programming device that is able to generate sufficient signal strength within a predefined space and maintain at least 20 to 30 dB of signal attenuation outside of that space. Such a device should ensure that only the designated tag receives a write command with sufficient strength for the transponder to act upon the command. When a programming device is properly designed, the chances for false programming can be minimized.
Tagging items with bar code labels and affixing boxes or containers with bar code shipping labels are standard business practices. Many companies who regularly use parcel service typically install a dedicated shipping software package, typically provided by the shipping carrier, and a bar code printer that prints on industry standard 4×6 inch stick-on thermal printing labels. While different carriers usually require different data formats or details, they universally require the originator's ID, a ship-to address, routing information, billing information, and tracking numbers. Bar codes alone may be adequate if one is willing to physically scan each and every package.
When the label becomes smeared with dirt, is damaged, faces the wrong direction, or is blocked by another piece of paper, the bar code alone becomes inadequate. When searching for a specific label within a pile of packages, the shortcomings of a bar code only system become blatantly obvious. In such situations, an RFID-based system provides a better solution than a bar code only system. For example, it is known that a package moving through the UPS™ system is scanned by a bar code scanner an average of 47 times between package acceptance and final package delivery. This means that a stationary or a handheld scanner must get close to the package and scan the package 47 times. On the other hand, an RFID-enabled system has the capability to greatly reduce human error in data collection, reduce inventory errors, improve product availability, identify and reduce loss and waste, and help ensure safety and security.
An industry trend is to migrate from a bar code only system to a system combining bar coded labels and RFID transponders. These systems retain the bar coded labels for circumstances when a human must visually inspect a shipping label to read the routing information, tracking numbers, and shipping destination. Therefore, the best migration path seems to be to laminate a thin RFID label behind the bar code label, and equip a standard bar code printer to simultaneously print the label and program the RFID label.
When installing an RFID reader/programmer capability in a standard bar code printer, one approach is to place a low gain antenna just before the bar code printing head. There are a few problems typically encountered when using this approach. First, there are usually many metal parts within the printer, which cause undesirable reflections and severe impedance mismatches—peaks and nulls in electromagnetic fields within the printer chassis. Because the RFID transponder programming device must utilize frequency hopping, peaks and nulls occur as the programmer hops from one frequency channel to another frequency channel. These peaks and nulls in the electromagnetic field are generally unpredictable. A second problem is that the antenna may read transponders that are placed far from the intended transponders when the antenna's field of surveillance becomes unpredictable.
A further complication is the fact that the industry's leading protocol is designed without any transponder personal identification numbers (PINs). This means in the blank mode, all transponders are identical. The programming device, therefore, loses its ability to confine its command to any specific set of transponders. The lack of a PIN means that when writing information to the transponder, any transponder exposed to minimum field strength will automatically respond to that programming command. There is no selection command to command that only a designated transponder will respond.
Since all commands will be received by all available transponders, it is the programmer's duty to ensure that only the designated transponder can receive an intended command and only the designated transponder should respond to such a command. In cases where two transponders are simultaneously within the reader's field of view, a write command may cause both transponders to accept the same write command, the same data, and the same lock command. Therefore, the possibility of having multiple transponders accept the same command and lock the same command is a real danger in a label printer designed to provide RFID transponder programmer.